7.3 Nuclear reactions, fission and fusion- Hyun Bin Lee & Daniel Leong
A nice intro video for fission and fusion and binding energy:
Nuclear reactions
7.3.1 Describe and give an example of an artificial (induced) transmutation.
Nuclear reaction is often called transmutation, because during the reaction, an atom changes from one element to another element.
example of transmutation reaction from Nitrogen-14 to Oxygen-17 is shown below.
This nuclear reaction is "balanced" so that the sums of the mass and atomic numbers are equal for both reactants and products.
7.3.3 Define the term unified atomic mass unit. Students must be familiar with the units MeVC¯² and GeVC¯² for mass.
7.3.4 Apply the Einstein mass-energy equivalence relationship.
In order to understand the concept of unified atomic mass unit, you first need to understand how the mass spectrometer works. It is explained in page 607 from Giancolli textbook and in wikipedia link below. The masses of nuclei can be determined using the mass spectrometer, and unified atomic mass unit (u) is a relative unit, because we compare masses of nuclei to that of Carbon-12 which has unified atomic mass unit of 12.000000 u. In other words, 1 u is equivalant to 1/12 of the mass of Carbon-12 atom, and it is similar to the mass of 1 proton (1.007276 u) or mass of 1 neutron. (1.008665 u)
Einstein equated mass and energy with E=mc² equation with a postlate that every matter which has mass has a certain amount of rest energy. Then, Einstein made a correlation between mass and energy with the equation E=mc², where E is energy, m is mass, and c is speed of light. From this equation, GeVC¯² and MeVC¯² can be derived as units of unified atomic mass unit. Energy is expressed in joules (J) and electron volts. Electron volt is defined as a unit of work requried for 1 electron to move thorugh a potential difference of 1 V. The charge on one electron is 1.6*10^-19 C. the mass can be expressed as GeV over c² or MeV over c² which are GeVc¯² and MeVc¯².
7.3.5 Define the concepts of mass defect, binding energy and binding energy per nucleon.
The mass of an atom and the sum of the masses individual components of that atom differs. For instance, the mass of a Helium-4 atom is 4.002602 u. Helium contains 2 protons, 2 electons, and 2 neutrons. However, the sum of the masses of 2 protons, 2 neutrons, and 2 electrons is only 4.032982 u. The sum of the parts is more massive than the atom. The difference between those two values is defined as the mass defect. The nucleus must have lesser mass than sum of its components in order to stay stable. Binding energy is energy which has been release when forming the nucleus. According to the law of conservation of matter, all mass should be conserved when individual components of an atom are assembled to form that atom. The binding energy is the mass defect which has been transformed in order to assemble the atom. Thus, the binding energy of the atom is calculated changing his equation into Eb=Δmc² where Eb is binding energy, Δm is mass defect and c is speed of light. Binding energy per nucleon is the value where binding energy is divided by number of nucleons. (number of protons and neutrons) This value allows the comparison of binding energy between different elements.
7.3.6 Draw and annotate a graph showing the variation with nucleon number of the binding energy per nucleon. Students should be familiar with binding energies plotted as positive quantities.
Curve of binding energy
The average binding energy per nucleon increases from hydrogen-1 atom as the number of nucleons in nucleus increases. However, after Iron-56 atom, the average binding energy per nucleon decreases as the number of nucleons in nucleus increases. Hence, Iron-56 atom has the highest average binding energy per nucleon.
7.3.8 Describe the processes of nuclear fission and nuclear fusion. Nuclear fusion is the process by which multiple like-charged atomic nuclei join together to form a heavier nucleus. It is accompanied by the release or absorption of energy (E=mc²). The fusion of two nuclei with lower mass than iron generally releases energy while the fusion of nuclei heavier than iron absorbs energy; vice-versa for the reverse process, nuclear fission.
When a nucleon such as a proton or neutron is added to a nucleus, the nuclear force attracts it to other nucleons, but primarily to its immediate neighbors due to the short range of the force. The nucleons in the interior of a nucleus have more neighboring nucleons than those on the surface. Since smaller nuclei have a larger surface area-to-volume ratio, the binding energy per nucleon due to the strong force generally increases with the size of the nucleus but approaches a limiting value corresponding to that of nucleus with a diameter of about four nucleons.The electrostatic force, on the other hand, is an inverse-square force, so a proton added to a nucleus will feel an electrostatic repulsion from all the other protons in the nucleus. The electrostatic energy per nucleon due to the electrostatic force thus increases without limit as nuclei get larger. The net result of these opposing forces is that the binding energy per nucleon generally increases with increasing size, up to the elements iron and nickel, and then decreases for heavier nuclei.
How Nuclear Fusion is being used today:
Nuclear Fission:
Nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts, often producing free neutrons and lighter nuclei, which may eventually produce photons (in the form of gamma rays). Fission of heavy elements is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments. Fission is a form of nuclear transmutation because the resulting fragments are not the same element as the original atom.
Nuclear fission differs from other forms of radioactive decay in that it can be harnessed and controlled via a chain reaction: free neutrons released by each fission event can trigger yet more events, which in turn release more neutrons and cause more fissions.Most nuclear fuels undergo spontaneous fission only very slowly, decaying mainly via an alpha/beta decay chain. In a nuclear reactor or nuclear weapon, most fission events are induced by bombardment with another particle such as a neutron.Typical fission events release about two hundred million eV of energy for each fission event.
Many heavy elements, such as uranium, thorium, and plutonium, undergo both spontaneous fission, a form of radioactive decay and induced fission, a form of nuclear reaction. Elemental isotopes that undergo induced fission when struck by a free neutron are called fissionable; isotopes that undergo fission when struck by a thermal, slow moving neutron are also called fissile. All fissionable and fissile isotopes undergo a small amount of spontaneous fission which releases a few free neutrons into any sample of nuclear fuel. Such neutrons would escape rapidly from the fuel and become a free neutron, with a half-life of about 15 minutes before they decayed to protons and beta particles. However, neutrons almost invariably impact and are absorbed by other nuclei in the vicinity long before this happens. Some neutrons will impact fuel nuclei and induce further fissions, releasing yet more neutrons. If enough nuclear fuel is assembled into one place, or if the escaping neutrons are sufficiently contained, then these freshly generated neutrons outnumber the neutrons that escape from the assembly, and a sustained nuclear chain reaction will take place.
Political issues:
Nuclear fission produces energy for nuclear power and to drive the explosion of nuclear weapons. Both uses are made possible because certain substances called nuclear fuels undergo fission when struck by free neutrons and in turn generate neutrons when they break apart. This makes possible a self-sustaining chain reaction that releases energy at a controlled rate in a nuclear reactor or at a very rapid uncontrolled rate in a nuclear weapon.
The amount of free energy contained in nuclear fuel is millions of times the amount of free energy contained in a similar mass of chemical fuel such as gasoline, making nuclear fission a very tempting source of energy; however, the products of nuclear fission are radioactive and remain so for significant amounts of time, giving rise to a nuclear waste problem. Concerns over nuclear waste accumulation and over the destructive potential of nuclear weapons may counterbalance the desirable qualities of fission as an energy source, and give rise to ongoing political debate over nuclear power.
Bibliography:
Wikipedia, Jan 5th, http://en.wikipedia.org/wiki/Main_Page
Physics - Fifth Edition, Giancoli, Prentice Hall, Jan 5th
ISB IB Physics Core Lecture Packet, David Young, Jan 5th
A nice intro video for fission and fusion and binding energy:
Nuclear reactions
7.3.1 Describe and give an example of an artificial (induced) transmutation.
Nuclear reaction is often called transmutation, because during the reaction, an atom changes from one element to another element.
example of transmutation reaction from Nitrogen-14 to Oxygen-17 is shown below.
This nuclear reaction is "balanced" so that the sums of the mass and atomic numbers are equal for both reactants and products.
Additional information on artificial transmutation from wikipedia:
http://en.wikipedia.org/wiki/Nuclear_transmutation
7.3.2 Construct and complete nuclear equations.
7.3.3 Define the term unified atomic mass unit.
Students must be familiar with the units MeVC¯² and GeVC¯² for mass.
7.3.4 Apply the Einstein mass-energy equivalence relationship.
In order to understand the concept of unified atomic mass unit, you first need to understand how the mass spectrometer works. It is explained in page 607 from Giancolli textbook and in wikipedia link below. The masses of nuclei can be determined using the mass spectrometer, and unified atomic mass unit (u) is a relative unit, because we compare masses of nuclei to that of Carbon-12 which has unified atomic mass unit of 12.000000 u. In other words, 1 u is equivalant to 1/12 of the mass of Carbon-12 atom, and it is similar to the mass of 1 proton (1.007276 u) or mass of 1 neutron. (1.008665 u)
Einstein equated mass and energy with E=mc² equation with a postlate that every matter which has mass has a certain amount of rest energy. Then, Einstein made a correlation between mass and energy with the equation E=mc², where E is energy, m is mass, and c is speed of light. From this equation, GeVC¯² and MeVC¯² can be derived as units of unified atomic mass unit. Energy is expressed in joules (J) and electron volts. Electron volt is defined as a unit of work requried for 1 electron to move thorugh a potential difference of 1 V. The charge on one electron is 1.6*10^-19 C. the mass can be expressed as GeV over c² or MeV over c² which are GeVc¯² and MeVc¯².
Additional information on unified atomic mass unit from wikipedia:
http://en.wikipedia.org/wiki/Atomic_mass_unit
7.3.5 Define the concepts of mass defect, binding energy and binding energy per nucleon.
The mass of an atom and the sum of the masses individual components of that atom differs. For instance, the mass of a Helium-4 atom is 4.002602 u. Helium contains 2 protons, 2 electons, and 2 neutrons. However, the sum of the masses of 2 protons, 2 neutrons, and 2 electrons is only 4.032982 u. The sum of the parts is more massive than the atom. The difference between those two values is defined as the mass defect. The nucleus must have lesser mass than sum of its components in order to stay stable. Binding energy is energy which has been release when forming the nucleus. According to the law of conservation of matter, all mass should be conserved when individual components of an atom are assembled to form that atom. The binding energy is the mass defect which has been transformed in order to assemble the atom. Thus, the binding energy of the atom is calculated changing his equation into Eb=Δmc² where Eb is binding energy, Δm is mass defect and c is speed of light. Binding energy per nucleon is the value where binding energy is divided by number of nucleons. (number of protons and neutrons) This value allows the comparison of binding energy between different elements.
Binding energy information from wikipedia:
http://en.wikipedia.org/wiki/Binding_energy
7.3.6 Draw and annotate a graph showing the variation with nucleon number of the binding energy per nucleon.
Students should be familiar with binding energies plotted as positive quantities.
The average binding energy per nucleon increases from hydrogen-1 atom as the number of nucleons in nucleus increases. However, after Iron-56 atom, the average binding energy per nucleon decreases as the number of nucleons in nucleus increases. Hence, Iron-56 atom has the highest average binding energy per nucleon.
7.3.8 Describe the processes of nuclear fission and nuclear fusion.
Nuclear fusion is the process by which multiple like-charged atomic nuclei join together to form a heavier nucleus. It is accompanied by the release or absorption of energy (E= mc²). The fusion of two nuclei with lower mass than iron generally releases energy while the fusion of nuclei heavier than iron absorbs energy; vice-versa for the reverse process, nuclear fission.
When a nucleon such as a proton or neutron is added to a nucleus, the nuclear force attracts it to other nucleons, but primarily to its immediate neighbors due to the short range of the force. The nucleons in the interior of a nucleus have more neighboring nucleons than those on the surface. Since smaller nuclei have a larger surface area-to-volume ratio, the binding energy per nucleon due to the strong force generally increases with the size of the nucleus but approaches a limiting value corresponding to that of nucleus with a diameter of about four nucleons.The electrostatic force, on the other hand, is an inverse-square force, so a proton added to a nucleus will feel an electrostatic repulsion from all the other protons in the nucleus. The electrostatic energy per nucleon due to the electrostatic force thus increases without limit as nuclei get larger. The net result of these opposing forces is that the binding energy per nucleon generally increases with increasing size, up to the elements iron and nickel, and then decreases for heavier nuclei.
How Nuclear Fusion is being used today:
Nuclear Fission:
Nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts, often producing free neutrons and lighter nuclei, which may eventually produce photons (in the form of gamma rays). Fission of heavy elements is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments. Fission is a form of nuclear transmutation because the resulting fragments are not the same element as the original atom.
Nuclear fission differs from other forms of radioactive decay in that it can be harnessed and controlled via a chain reaction: free neutrons released by each fission event can trigger yet more events, which in turn release more neutrons and cause more fissions.Most nuclear fuels undergo spontaneous fission only very slowly, decaying mainly via an alpha/beta decay chain. In a nuclear reactor or nuclear weapon, most fission events are induced by bombardment with another particle such as a neutron.Typical fission events release about two hundred million eV of energy for each fission event.
Many heavy elements, such as uranium, thorium, and plutonium, undergo both spontaneous fission, a form of radioactive decay and induced fission, a form of nuclear reaction. Elemental isotopes that undergo induced fission when struck by a free neutron are called fissionable; isotopes that undergo fission when struck by a thermal, slow moving neutron are also called fissile. All fissionable and fissile isotopes undergo a small amount of spontaneous fission which releases a few free neutrons into any sample of nuclear fuel. Such neutrons would escape rapidly from the fuel and become a free neutron, with a half-life of about 15 minutes before they decayed to protons and beta particles. However, neutrons almost invariably impact and are absorbed by other nuclei in the vicinity long before this happens. Some neutrons will impact fuel nuclei and induce further fissions, releasing yet more neutrons. If enough nuclear fuel is assembled into one place, or if the escaping neutrons are sufficiently contained, then these freshly generated neutrons outnumber the neutrons that escape from the assembly, and a sustained nuclear chain reaction will take place.
Political issues:
Nuclear fission produces energy for nuclear power and to drive the explosion of nuclear weapons. Both uses are made possible because certain substances called nuclear fuels undergo fission when struck by free neutrons and in turn generate neutrons when they break apart. This makes possible a self-sustaining chain reaction that releases energy at a controlled rate in a nuclear reactor or at a very rapid uncontrolled rate in a nuclear weapon.
The amount of free energy contained in nuclear fuel is millions of times the amount of free energy contained in a similar mass of chemical fuel such as gasoline, making nuclear fission a very tempting source of energy; however, the products of nuclear fission are radioactive and remain so for significant amounts of time, giving rise to a nuclear waste problem. Concerns over nuclear waste accumulation and over the destructive potential of nuclear weapons may counterbalance the desirable qualities of fission as an energy source, and give rise to ongoing political debate over nuclear power.
Bibliography:
Wikipedia, Jan 5th, http://en.wikipedia.org/wiki/Main_Page
Physics - Fifth Edition, Giancoli, Prentice Hall, Jan 5th
ISB IB Physics Core Lecture Packet, David Young, Jan 5th